At 6ft 8in and weighing in at 115kg , Galarza will provide Nigel Davies with additional second row options as Gloucester's Director of Rugby aims to create strength in depth in every position.
Galarza has, to date, made 18 appearances for the Pumas after making his debut in 2010 and was involved in their Rugby World Cup 2011 campaign.
A student of medicine, Galarza spent time with Leinster Rugby in 2010-11, before returning to his homeland to play for the prestigious Pampas XV in the Vodacom Cup.
Nigel Davies spoke of his delight of having secured another experienced international for next year's squad.
"Our search for second rows has been detailed. Having Alex Brown involved in the process has been crucial, as he obviously has a huge amount of expertise in this area.
"We're delighted to have secured Mariano's services, as his qualities will complement the players we already have in place and give us some genuine options in the second row.
"Having spoken with Mariano, he is excited at the prospect of becoming a Gloucester player and is looking forward to becoming part of what is shaping up to be an exciting squad of players.
"I believe this gives us plenty of strength and depth in a hugely important area of the squad as we seek to establish a powerful forward platform for next season. Mariano is an experienced, physical operator and his signing is another statement of intent for us."